1. Field of the Invention
This invention relates to semiconductor device manufacturing, and more particularly, to a magnetic field shield layer and a method for making the same.
2. Description of the Related Art
The following descriptions and examples are given as background only.
Several conditions may affect the operation of a semiconductor device. In particular, the ambient to which a device is exposed may affect the operation of a device. For example, exposure to extremely low or high temperatures may adversely affect the operation of a device. In addition or alternatively, the presence of stray or external magnetic fields may affect the functionality of a device. In particular, exposure to external magnetic fields may be particularly harmful for devices that include magnetoresistive memory cells, such as giant magnetoresistance (GMR) memory cells or magnetic tunnel junction (MTJ) memory cells. In general, magnetoresistive memory cells function by the application of magnetic field vectors. Magnetic field vectors applied over a particular threshold limit may cause a change in resistance by which states of a cell (“0” and “1”) may be switched and by which the read and write operations of a device may be defined.
Preferably, the magnetic field vectors applied to a memory cell are generated by the integrated circuitry of the device comprising the cell such that the application of the fields may be controlled. In particular, the magnetic field vectors used to switch the state of a memory cell are preferably generated by current directed along the bit and/or digit lines of the device. External or stray magnetic fields, however, may cause states of the cell to switch independently of the magnetic field vectors generated from the device, causing the device to malfunction. “External” or “stray” magnetic fields may refer to magnetic field vectors that are present in the ambient of a device, distinct from those vectors that are generated by the circuitry of the device. Such external or stray magnetic fields may originate from a plurality of sources, such as neighboring electrical devices, for example. In addition, the thresholds at which states of cells switch continues to decrease as cell dimensions continue to decrease. Consequently, lower magnetic fields, including those applied by the circuitry of the device and external sources, may be capable of changing the states of memory cells with such decreased dimensions.
Furthermore, external or stray magnetic fields may be applied at any angle with respect to the memory cell. In general, magnetic field vectors applied either parallel or antiparallel across a junction of a magnetoresistive memory cell may cause a change in resistance within the cell, thereby causing the states of the cell to switch. Such an application of magnetic field vectors may be from external magnetic fields alone or in conjunction with magnetic field vectors generated by currents along the bit and digit lines as described above. In some cases, magnetoresistive memory cells may be designed such that switching of states may be easier with magnetic field vectors applied in one direction versus another direction. A memory cell with such adaptation may be configured in any shape, which has a longer dimension in one direction versus a second dimension of the shape. In such an embodiment, the direction by which magnetic fields may be applied such that switching is more easily obtained may be referred to as the “easy” axis. Such a direction may refer to the elongated portion of the memory cell. The respective shorter dimension of the memory cell may be referred to as the “hard” axis and may refer to the direction by which magnetic fields may be applied such that switching of the states of the cell is more difficult to obtain. Consequently, external magnetic fields applied along the easy axis of a magnetoresistive memory cell may be particularly harmful to the operation of a device comprising the memory cell.
It would therefore be desirable to develop a device that is shielded from external or stray magnetic fields. In particular, it may be advantageous to develop a device in which the easy axis of a memory cell is shielded. In other cases, it may be advantageous to fabricate a device in which the hard axis of the memory cell is additionally or alternatively shielded. In yet another embodiment, it may be desirable to develop a device that is shielded along any direction of a memory cell. Such an embodiment may be particularly advantageous for devices with memory cells that do not have easy and hard axes orientations.